The present invention relates to high explosive grain fill in projectiles and, more particularly, to apparatus for preventing the premature detonation of such high explosive fill due to peak acceleration during launch of the projectile.
High explosive projectiles, and particularly gun-launched high explosive filled projectiles experience exceedingly high peak accelerations during launch thereof. These accelerations are sufficient under some circumstances to cause premature explosion in the bore of the gun.
Such premature explosions are believed to be caused by the presence of high axial stress in the high explosive grain, possibly coupled with lateral or radial acceleration due to spin.
The tendency to premature explosion is believed to be increased by the use of more sensitive (and more powerful) explosive such as Composition B instead of TNT. Other causes of premature explosion may include defects in the explosive grain in the presence of large stresses, gaps between the high explosive grain and the body at the rear of the projectile which become compressed by large deformation of the explosive grain due to the high stresses and forces during firing, and both axial and torsional slip between the side wall of the shell body and the high explosive grain.
Although the above failure mechanisms are believed by the inventor to be factors in producing premature explosion of high explosive grain in gun-fired projectiles, it should not be assumed either that this list is exhaustive nor that the present invention is limited by the above noted theories.
Possible methods of avoiding premature explosion may include the use of less sensitive explosives, for example, the use of TNT rather than the more powerful and sensitive Comp B. This solution reduces the lethality and effectiveness of the explosive charge. Another possible solution is to limit the acceleration at which the projectile can be fired. This, of course, results in reduced range capability of the weapon system. Premature explosion from faults in the explosive grain may also be, in theory, avoided by greater care in manufacture and casting of the explosive grain in the projectile casing. Although this method may be used in research and exploratory development activities, it is probably too expensive in a normal production environment. A further possibility is to bond the grain to the casing in order to cause the axial setback force in the high explosive grain to be transmitted to the body of the projectile due to the large mismatch in modulus of the two materials. The effectiveness of such glue bonding is limited by aging effects of the glue itself as well as deleterious effects on the bonding due to thermal cycling and mishandling during long storage. In addition, undesired chemical reactions may take place between the high explosive grain and the components of the glue. These undesired effects of glue bonding may lead to cracking of the explosive grain either from residual manufacturing stresses or thermal and mechanical stresses during temperature cycling caused by the mismatch in bulk thermal expansion coefficient between the high explosive grain and the steel projectile body. Thus actual or incipient failure of the glue bond prior to firing may still cause premature detonation. Furthermore, such potential for premature high explosive grain detonation also may present a hazard during accidental drops of the projectiles during handling.